Timing signal generation device and electronic apparatus

ABSTRACT

A timing signal generation device includes: an output terminal that outputs a standard signal; a first standard signal generation unit that generates a first standard signal based on a reference signal input from outside; a second standard signal generation unit that generates a second standard signal based on a signal output from an oscillator; and a control unit that switches the standard signal output from the output terminal from the first standard signal to the second standard signal based on prior information indicating that accuracy of the reference signal deteriorates.

CROSS REFERENCE

This application claims benefit of Japanese Application No. 2015-054045,filed on Mar. 17, 2015. The disclosure of the prior application ishereby incorporated by reference herein in its entirety.

BACKGROUND 1. Technical Field

The present invention relates to a timing signal generation device andan electronic apparatus.

2. Related Art

The global positioning system (GPS) which is one of the globalnavigation satellite systems (GNSS) using artificial satellites iswidely known. Atomic clocks with considerably high accuracy are mountedon GPS satellites used for the GPS. Satellite signals on whichtrajectory information of GPS satellites or accurate time information orthe like is superimposed are transmitted to the ground. The satellitesignals transmitted from the GPS satellites are received by GPSreceivers. Then, the GPS receivers perform a process of calculating timeinformation or the current positions of the GPS receivers based on thetrajectory information or the time information superimposed on thesatellite signals or a process of generating accurate timing signals (1PPS) synchronized with coordinated universal time (UTC) or the like.

In such GPS receivers, a normal positioning (position estimation) modeproviding a position and a time based on positioning calculation and aposition fixing mode supplying a time by fixing positioning at a knownposition are generally provided.

In the normal positioning mode, satellite signals from GPS satellitesequal to or greater than a predetermined number (minimum threesatellites in the case of 2-dimensional positioning and four satellitesin the case of 3-dimensional positioning) are necessary. As the numberof GPS satellites capable of receiving satellite signals is larger, theaccuracy of positioning calculation is further improved.

In the position fixing mode, when position information of a GPS receiveris set and a satellite signal from at least one GPS satellite can bereceived, a 1 PPS can be generated.

JP-A-8-105984 discloses a 1-second signal acquisition device thatreceives ranging radio waves transmitted from a plurality of artificialsatellites and generates a 1 PPS (standard signal).

The 1-second signal acquisition device includes an antenna 2 thatreceives ranging radio waves transmitted from a plurality of artificialsatellites 1, a GPS receiver 3 that is connected to the antenna 2, a 1PPS validity determination unit 4 that is connected to the GPS receiver3, a state determination unit 5 that is connected to the GPS receiver 3and the 1 PPS validity determination unit 4, a timing circuit 6 that isconnected to the 1 PPS validity determination unit 4 and the statedetermination unit 5, and a reference oscillator 7 in the device that isconnected to the timing circuit 6, the PPS validity determination unit4, and the state determination unit 5. A load-side device 8 such as atime-related device is connected to the timing circuit 6. The 1 PPSvalidity determination unit 4 determines validity of a 1 PPS output fromthe GPS receiver 3, that is, whether the 1 PPS is continuous at acorrect timing of 1 Hz.

When the 1 PPS is valid, the 1-second signal acquisition device outputsa 1 PPS output from the GPS receiver 3. When the 1 PPS is not valid, the1-second signal acquisition device outputs a 1 PPS output from thereference oscillator 7 in the device.

In the 1-second signal acquisition device disclosed in JP-A-8-105984,however, even when the 1 PPS is not valid, the 1 PPS output from the GPSreceiver 3 is output in some cases during the determination regardingwhether the 1 PPS output from the GPS receiver 3 is valid. Therefore,there is the problem that accuracy of the 1 PPS may not be ensured.

SUMMARY

An advantage of some aspects of the invention is to provide a timingsignal generation device and an electronic apparatus capable of ensuringtemporal accuracy of a standard signal.

The invention can be implemented as the following forms or applicationexamples.

Application Example 1

A timing signal generation device according to this application exampleincludes: an output terminal that outputs a standard signal; a firststandard signal generation unit that generates a first standard signalbased on a reference signal input from outside; a second standard signalgeneration unit that generates a second standard signal based on asignal output from an oscillator; and a control unit that switches thestandard signal output from the output terminal from the first standardsignal to the second standard signal based on prior informationindicating that accuracy of the reference signal deteriorates.

With this configuration, the standard signal can be switched from thefirst standard signal to the second standard signal before accuracy ofthe reference signal deteriorates more than the lower limit of anallowable range. Accordingly, it is possible to ensure temporal accuracyof the standard signal.

Application Example 2

It is preferable that the timing signal generation device according tothe application example further includes a prior information output unitthat outputs the prior information to the control unit.

With this configuration, the control unit switches the standard signalfrom the first standard signal to the second standard signal based onthe prior information before the accuracy of the reference signaldeteriorates more than the lower limit of the allowable range.

Application Example 3

In the timing signal generation device according to the applicationexample, it is preferable that the prior information output unitincludes a prior information storage unit that stores the priorinformation.

With this configuration, by using the prior information stored in theprior information storage unit, it is possible to omit an effort toinput the prior information every time.

Application Example 4

In the timing signal generation device according to the applicationexample, it is preferable that the prior information output unitincludes a prior information generation unit that generates the priorinformation based on the reference signal in advance.

With this configuration, it is possible to obtain more accurate priorinformation.

Application Example 5

It is preferable that the timing signal generation device according tothe application example further includes a time information storage unitthat stores time information. The control unit preferably includes aswitch timing decision unit that decides a switch timing of the standardsignal based on the prior information and the time information.

With this configuration, before the accuracy of the reference signaldeteriorates more than the lower limit of the allowable range, it ispossible to set any switch timing of the standard signal.

Application Example 6

In the timing signal generation device according to the applicationexample, it is preferable that the reference signal is a satellitesignal transmitted from a position information satellite, the priorinformation output unit outputs DOP information indicating a relationbetween a time and an accuracy deterioration rate of positioning basedon the reference signal as information indicating that the accuracy ofthe reference signal deteriorates to the switch timing decision unit,and the switch timing decision unit includes a threshold value storageunit that stores a threshold value and decides the switch timing of thestandard signal based on the threshold value and the DOP information.

With this configuration, until an accuracy deterioration rate ofpositioning based on the reference signal becomes a certain value, it ispossible to arbitrarily set whether the first standard signal is outputas the standard signal.

Application Example 7

In the timing signal generation device according to the applicationexample, it is preferable that the oscillator is a voltage controloscillator, the first standard signal generation unit inputs a controlvoltage of the oscillator to the oscillator and generates the firststandard signal based on the reference signal when the accuracydeterioration rate is equal to or less than the threshold value, and thecontrol unit acquires information regarding a control voltage of theoscillator input to the oscillator when the accuracy deterioration rateis equal to or less than the threshold value, and the control unitobtains a control voltage input to the oscillator based on the acquiredinformation regarding the control voltage and inputs the obtainedcontrol voltage to the oscillator to switch the reference signal outputfrom the output terminal from the first standard signal to the secondstandard signal when the accuracy deterioration rate exceeds thethreshold value.

With this configuration, when the second standard signal is output,aging correction of the oscillator can be performed. Therefore, it ispossible to improve the temporal accuracy of the second standard signal.

Application Example 8

In the timing signal generation device according to the applicationexample, it is preferable that the reference signal is a satellitesignal transmitted from a position information satellite, and the firststandard signal generation unit preferably includes a receiver thatreceives the satellite signal.

With this configuration, it is possible to receive the satellite signalsand generate the first standard signal.

Application Example 9

In the timing signal generation device according to the applicationexample, it is preferable that the prior information includesinformation indicating that the accuracy of the reference signalimproves, and the control unit switches the standard signal output fromthe output terminal from the second standard signal to the firststandard signal based on the prior information.

With this configuration, when the accuracy of the reference signaldeteriorates more than the lower limit of the allowable range andsubsequently becomes equal to or greater than the lower limit, it ispossible to switch the standard signal from the second standard signalto the first standard signal. Accordingly, it is possible to furtherimprove the temporal accuracy of the standard signal.

Application Example 10

A timing signal generation device according to this application exampleswitches, based on prior information indicating that accuracy of areference signal input from outside deteriorates, a signal used togenerate a standard signal from the reference signal to a signal outputfrom an internal oscillator.

With this configuration, it is possible to switch the standard signalfrom the first standard signal to the second standard signal before theaccuracy of the reference signal deteriorates more than the lower limitof the allowable range. Accordingly, it is possible to ensure thetemporal accuracy of the standard signal.

Application Example 11

An electronic apparatus according to this application example includesthe timing signal generation device according to the applicationexample.

With this configuration, it is possible to switch the standard signalfrom the first standard signal to the second standard signal before theaccuracy of the reference signal deteriorates more than the lower limitof the allowable range. Accordingly, it is possible to ensure thetemporal accuracy of the standard signal.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a diagram illustrating a schematic configuration of a firstembodiment of a timing signal generation device according to theinvention.

FIGS. 2A to 2C are diagrams illustrating the configuration of anavigation message transmitted from a GPS satellite.

FIG. 3 is a block diagram illustrating an example of the configurationof a GPS receiver included in the timing signal generation deviceillustrated in FIG. 1.

FIG. 4 is a graph illustrating a relation between a time and an accuracydeterioration rate of a satellite signal in the timing signal generationdevice illustrated in FIG. 1.

FIG. 5 is a graph illustrating a relation between a time and a controlvoltage obtained based on the satellite signal and input to a crystaloscillator in the timing signal generation device illustrated in FIG. 1.

FIG. 6 is a diagram illustrating a schematic configuration of main unitsof a second embodiment of the timing signal generation device accordingto the invention.

FIG. 7 is a graph illustrating a relation between a time and an accuracydeterioration rate of a satellite signal in the timing signal generationdevice illustrated in FIG. 6.

FIG. 8 is a block diagram illustrating an embodiment of an electronicapparatus according to the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a timing signal generation device and an electronicapparatus according to the invention will be described in detailaccording to embodiments illustrated in the appended drawings.

1. Timing Signal Generation Device First Embodiment

FIG. 1 is a diagram illustrating a schematic configuration of a firstembodiment of a timing signal generation device according to theinvention. FIGS. 2A to 2C are diagrams illustrating the configuration ofa navigation message transmitted from a GPS satellite. FIG. 3 is a blockdiagram illustrating an example of the configuration of a GPS receiverincluded in the timing signal generation device illustrated in FIG. 1.FIG. 4 is a graph illustrating a relation between a time and an accuracydeterioration rate of a satellite signal in the timing signal generationdevice illustrated in FIG. 1. FIG. 5 is a graph illustrating a relationbetween a time and a control voltage obtained based on the satellitesignal and input to a crystal oscillator in the timing signal generationdevice illustrated in FIG. 1.

A timing signal generation device 1 illustrated in FIG. 1 includes a GPSreceiver (receiver) 10 serving as a satellite signal reception unit, aprocessing unit (CPU) 20 serving as a satellite signal reception controldevice, a crystal oscillator (oscillator) 30 serving as a voltagecontrol oscillator (VCO), a temperature sensor 40, a control unit 31, atimer (clock) 32, a prior information output unit 33, and a GPS antenna50.

Some or all of the constituent elements of the timing signal generationdevice 1 may be physically separated or may be integrated. For example,the GPS receiver 10 and the processing unit 20 may be realized byseparate ICs. The GPS receiver 10 and the processing unit 20 may berealized by one IC. The same applies to the other portions.

The timing signal generation device 1 receives signals transmitted fromGPS satellites (positional information satellites) 2 and generates ahighly accurate 1 PPS.

The GPS satellites 2 orbit along predetermined trajectories above theearth and transmit satellite signals (GPS signals) in which navigationmessages and coarse/acquisition codes (C/A codes) are superimposed(carrier waves are modulated) on radio waves (L1 waves) with 1.57542 GHzwhich are carrier waves to the ground. The satellite signal is anexample of a reference signal input from the outside to the timingsignal generation device 1.

The C/A codes are used to identify the satellite signals of the GPSsatellites 2 which are currently about 30 satellites and are uniquepatterns formed from 1023 chips (a period of 1 ms) for which each chipis one of +1 and −1. Accordingly, by taking a correlation of thesatellite signal and the pattern of each C/A code, it is possible todetect the C/A code superimposed on the satellite signal.

The satellite signal (specifically, a navigation message) transmitted byeach GPS satellite 2 includes trajectory information indicating theposition of each GPS satellite 2 along the trajectory. An atomic clockis mounted on each GPS satellite 2 and the satellite signal includesconsiderably accurate time information clocked by the atomic clock.Accordingly, by receiving the satellite signals from four or more of theGPS satellites 2 and performing positioning calculation using thetrajectory information and the time information included in eachsatellite signal, it is possible to obtain accurate informationregarding the position and time of a reception point (an installationplace of the GPS antenna 50). Specifically, a quartic equation that has3-dimensional positions (x, y, z) and a time t of a reception point asfour variables may be established to obtain its solution.

When the position of the reception point is known, the satellite signalscan be received from one or more of the GPS satellites 2 and the timeinformation of the reception point can be obtained using timeinformation included in each satellite signal.

Information regarding a difference between the time of each GPSsatellite 2 and the time of the reception point can be obtained usingthe trajectory information included in each satellite signal. A slighttime error between the atomic clocks mounted on the GPS satellites 2 ismeasured by a control segment on the ground and a time correctionparameter for correcting the time error is also included in thesatellite signal. By correcting the time of the reception point usingthe time correction parameter, it is possible to obtain the considerablyaccurate time information.

As illustrated in FIG. 2A, the navigation message is configured toinclude data for which a main frame of a total number of 1500 bits isone unit. The main frame is divided into five subframes 1 to 5 whicheach have 300 bits. Data of one subframe is transmitted in 6 secondsfrom each GPS satellite 2. Accordingly, the data of one main frame istransmitted in 30 seconds from each GPS satellite 2.

The subframe 1 includes satellite correction data such as week numberdata (WN). The week number data is information that indicates a weekincluding a time of the GPS satellite 2. A starting point of the time ofthe GPS satellite 2 is 00:00:00, 6 Jan. 1980 of the UTC (the worldstandard time) and a week starting from that day has a week number of 0.The week number data is updated in units of one week.

The subframes 2 and 3 include an ephemeris parameter (detailedtrajectory information of each GPS satellite 2). The subframes 4 and 5include an almanac parameter (schematic trajectory information of allthe GPS satellites 2).

The head of each of the subframes 1 to 5 includes a TLM (Telemetry) wordin which telemetry word (TLM) data of 30 bits are stored and a HOW wordin which handover word (HOW) data of 30 bits are stored.

Accordingly, the TLM word and the HOW word are transmitted at intervalsof 6 seconds from the GPS satellites 2, and the satellite correctiondata such as the week number data, the ephemeris parameter, and analmanac parameter are transmitted at intervals of 30 seconds.

As illustrated in FIG. 2B, the TLM word includes preamble data, a TLMmessage, reserved bits, and parity data.

As illustrated in FIG. 2C, the HOW word includes time information calledtime of week (TOW) (hereinafter also referred to as a “Z count”). In Zcount data, an elapsed time is displayed in seconds from 00:00:00 ofevery Sunday and is returned to 0 at 00:00:00 on the following Sunday.That is, the Z count data is information in units of seconds indicatedfrom the beginning of a week once a week and the elapsed time is anumber expressed in units of 1.5 seconds. Here, the Z count dataindicates time information in which the first bit of subsequent subframedata is transmitted. For example, the Z count data of the subframe 1indicates time information in which the first bit of the subframe 2 istransmitted. The HOW word includes 3-bit data (ID code) indicating theID of the subframe. That is, the HOW words of the subframes 1 to 5illustrated in FIG. 2A respectively include the ID codes of “001”,“010”, “011”, “100”, and “101”.

By acquiring the week number data included in the subframe 1 and the HOWwords (Z count data) included in the subframes 1 to 5, it is possible tocalculate the time of the GPS satellite 2. When the week number data isacquired previously and the elapsed time from a period in which the weeknumber data is acquired is counted internally, the current week numberdata of the GPS satellite 2 can be obtained even without acquiring theweek number data every time. Accordingly, when only the Z count data isacquired, the current time of the GPS satellite 2 can be approximatelyestimated.

The above-described satellite signals are received by the GPS receiver10 via the GPS antenna 50 illustrated in FIG. 1.

The GPS antenna 50 is an antenna that receives various radio wavesincluding the satellite signals and is connected to the GPS receiver 10.

The GPS receiver 10 performs various processes based on the satellitesignals received via the GPS antenna 50.

Specifically, the GPS receiver 10 has a normal positioning mode (firstmode) and a position fixing mode (second mode) and is set to one of thenormal positioning mode and the position fixing mode according to acontrol command (a control command for mode setting) from the processingunit (CPU) 20.

In the normal positioning mode, the GPS receiver 10 functions as a“positioning calculation unit”, receives the satellite signalstransmitted from the plurality of GPS satellites 2 (preferably, four ormore of the GPS satellites), and performs positioning calculation basedon the trajectory information (specifically, the ephemeris data, thealmanac data, and the like described above) and the time information(specifically, the week number data, the Z count data, and the likedescribed above) included in the received satellite signals. The GPSreceiver 10 generates a 1 PPS to be described below.

In the position fixing mode, the GPS receiver 10 functions as a “timingsignal generation unit”, receives the satellite signals transmitted fromone or more of the GPS satellites 2, and generates a 1 pulse per second(1 PPS) based on the trajectory information and the time informationincluded in the received satellite signals and the positionalinformation of the set reception point. The 1 PPS (which is an exampleof a timing signal synchronized with a reference time) is a pulse signalwhich is completely synchronized with the UTC (the world standard time),and includes 1 pulse per second. In this way, when the satellite signalsused for the GPS receiver 10 to generate the timing signal include thetrajectory information and the time information, the timing signalaccurately synchronized with the reference time can be generated.

Hereinafter, the configuration of the GPS receiver 10 will be describedin detail.

The GPS receiver 10 illustrated in FIG. 3 includes a surface acousticwave (SAW) filter 11, an RF processing unit 12, a baseband processingunit 13, and a temperature compensated crystal oscillator (TCXO) 14.

The SAW filter 11 performs a process of extracting the satellite signalsfrom the radio waves received by the GPS antenna 50. The SAW filter 11is configured as a bandpass filter that passes a signal of 1.5 GHzbandwidth.

The RF processing unit 12 includes a phase locked loop (PLL) 121, a lownoise amplifier (LNA) 122, a mixer 123, an IF amplifier 124, anintermediate frequency (IF) filter 125, and an A/D converter (ADC) 126.

The PLL 121 generates a clock signal in which an oscillation signal ofthe TOXO 14 oscillating at about a few MHz is multiplied by a frequencyof 1.5 GHz bandwidth.

The satellite signals extracted by the SAW filter are amplified by theLNA 122. The satellite signals amplified by the LNA 122 are mixed withthe clock signal output by the PLL 121 in the mixer 123 to bedown-converted to a signal (IF signal) with an intermediate frequencybandwidth (for example, a few MHz). The signal mixed by the mixer 123 isamplified by the IF amplifier 124.

Since a high frequency signal of a GHz order is generated along with theIF signal through the mixing by the mixer 123, the IF amplifier 124 alsoamplifies the high frequency signal along with the IF signal. The IFfilter 125 passes the IF signal and removes the high frequency signal(precisely, attenuates the high frequency signal to a level equal to orless than a predetermined level). The IF signal which has passed throughthe IF filter 125 is converted into a digital signal by the A/Dconverter (ADC) 126.

The baseband processing unit 13 includes a digital signal processor(DSP) 131, a central processing unit (CPU) 132, a static random accessmemory (SRAM) 133, and a real time clock (RTC) 134 and performs variousprocesses using the oscillation signal of the TCXO 14 as a clock signal.

The DSP 131 and the CPU 132 cooperate to demodulate the baseband signalfrom the IF signal, acquire the trajectory information or the timeinformation included in the navigation message, and perform a process ofthe normal positioning mode or a process of the position fixing mode.

The SRAM 133 stores the acquired time information and trajectoryinformation, the positional information of the reception point setaccording to a predetermined control command (a control command forposition setting), an elevation angle mask used in the position fixingmode or the like. The RTC 134 generates a timing at which basebandprocessing is performed. The RTC 134 is up-counted with the clock signalfrom the TCXO 14.

Specifically, the baseband processing unit 13 performs a process(satellite searching) of generating a local code with the same patternas each C/A code and taking correlation between the local code and eachC/A code included in the baseband signal. Then, the baseband processingunit 13 adjusts a generation timing of the local code so that thecorrelation value with each local code is peak and determines that thelocal code is synchronized with the GPS satellite 2 using the C/A code(captures the GPS satellite 2) when a correlation value is equal to orgreater than a threshold value. In the GPS, a code division multipleaccess (CDMA) scheme is adopted in which all of the GPS satellites 2transmit the satellite signals with the same frequency using differentC/A codes. Accordingly, by determining the C/A codes included in thereceived satellite signals, it is possible to search for the GPSsatellites 2 which can be captured.

The baseband processing unit 13 performs a process of mixing thebaseband signal and the local code with the same pattern as the C/A codeof the captured GPS satellite 2 to acquire the trajectory informationand the time information of this GPS satellite 2. The navigation messageincluding the trajectory information and the time information of thecaptured GPS satellite 2 is demodulated to the mixed signal. Then, thebaseband processing unit 13 performs a process of acquiring thetrajectory information and the time information included in thenavigation message and storing the trajectory information and the timeinformation in the SRAM 133.

The baseband processing unit 13 receives the predetermined controlcommand (specifically, the control command for the mode setting) and isset to either the normal positioning mode or the position fixing mode.In the normal positioning mode, the baseband processing unit 13 performsthe positioning calculation using the trajectory information and thetime information of four or more of the GPS satellites 2 stored in theSRAM 133.

In the position fixing mode, the baseband processing unit 13 outputs thehighly accurate 1 PPS using the trajectory information of one or more ofthe GPS satellites 2 stored in the SRAM 133 and the positionalinformation of the reception point stored in the SRAM 133. Specifically,the baseband processing unit 13 includes a 1 PPS counter that counts ageneration timing of each pulse of the 1 PPS in a part of the RTC 134,calculates a propagation delay time necessary for the satellite signaltransmitted from the GPS satellite 2 to arrive at the reception pointusing the trajectory information of the GPS satellite 2 and thepositional information of the reception point, and changes a set valueof the 1 PPS counter to an optimum value based on the propagation delaytime.

In the normal positioning mode, the baseband processing unit 13 outputsthe 1 PPS based on the time information of the reception point obtainedthrough the positioning calculation.

In the position fixing mode, the positioning calculation may beperformed when the plurality of GPS satellites 2 can be captured.

The baseband processing unit 13 outputs NMEA data including variouskinds of information such as positional information or time informationof the result of the positioning calculation and a reception status (thenumber of captured GPS satellites 2, the intensities of the satellitesignals, and the like).

The operation of the GPS receiver 10 having the above-describedconfiguration is controlled by the processing unit (CPU) 20 illustratedin FIG. 1.

The processing unit 20 transmits various control commands on the GPSreceiver 10, controls the operation of the GPS receiver 10, and receivesthe 1 PPS and the NMEA data, and performs various processes output bythe GPS receiver 10. For example, the processing unit 20 may performvarious processes according to programs stored in any memory.

The processing unit 20 includes a phase comparator 21, a loop filter 22,a digital signal processor (DSP: position information generation unit)23, a frequency divider 24, and a GPS control unit (reception controlunit) 25. The DSP 23 and the GPS control unit 25 may be configured byone component.

The DSP 23 acquires the NMEA data from the GPS receiver 10 periodically(for example, per second), collects positional information (the resultof the positioning result in the normal positioning mode by the GPSreceiver 10) including the NMEA data to generate statistical informationat a predetermined time, and performs a process of generating thepositional information of the reception point based on the statisticalinformation. In particular, the positional information of the receptionpoint is generated based on a representative value (for example, anaverage value, a mode, or a median value) of the plurality ofpositioning calculation results in the normal positioning mode by theGPS receiver 10.

The GPS control unit 25 transmits various control commands to the GPSreceiver 10 and controls the operation of the GPS receiver 10.Specifically, the GPS control unit 25 transmits the control command forthe mode setting to the GPS receiver 10 and performs a process ofswitching the mode of the GPS receiver 10 from the normal positioningmode to the position fixing mode. The GPS control unit 25 transmits thecontrol command for the position setting before the switching of themode of the GPS receiver 10 from the normal positioning mode to theposition fixing mode to the GPS receiver 10 and performs a process ofsetting the positional information of the reception point generated bythe DSP 23 in the GPS receiver 10.

The frequency divider 24 performs f (where f is a frequency) division onthe clock signal output by the crystal oscillator 30 and outputs thefrequency-divided clock signal of 1 Hz.

The phase comparator 21 compares the phases of the 1 PPS output by theGPS receiver 10 and the frequency-divided clock signal of 1 Hz output bythe frequency divider 24. A phase difference signal of a comparisonresult of the phase comparator 21 is input to the crystal oscillator 30via the loop filter 22. The parameter of the loop filter 22 is set bythe DSP 23.

The frequency-divided clock signal of 1 Hz output by the frequencydivider 24 is synchronized with the 1 PPS output by the GPS receiver 10,and the timing signal generation device 1 outputs the frequency-dividedclock signal as the 1 PPS with considerably high accuracy synchronizedwith the UTC to the outside. The 1 PPS is referred to as a “firststandard signal”. The GPS receiver 10, the processing unit 20, and thecrystal oscillator 30 form main units of a first standard signalgeneration unit.

Under the control of the control unit 31, the processing unit 20 stopsthe process of synchronizing the clock signal output by the crystaloscillator 30 to the 1 PPS output by the GPS receiver 10, stopsoutputting the first standard signal, causes the crystal oscillator 30to perform free-running oscillation, and outputs the 1 PPS to theoutside instead of the first standard signal. The 1 PPS is referred toas “second standard signal”. The crystal oscillator 30 and the frequencydivider 24 form main units of a second standard signal generation unit.

The switch between the first and second standard signals is performedbased on the prior information to be described below, which will bedescribed in detail below.

When a situation (holdover) in which the GPS receiver 10 may not receivethe satellite signals other than an assumed situation occurs, theaccuracy of the 1 PPS output by the GPS receiver 10 deteriorates or theoutputting of the 1 PPS by the GPS receiver 10 is stopped. However, evenin this case, the second standard signal may be output.

The timing signal generation device 1 outputs the recent NMEA data persecond to the outside in synchronization with the 1 PPS and outputs theclock signal with the frequency of f output by the crystal oscillator 30to the outside.

The crystal oscillator 30 is not particularly limited and, for example,a thermostatic chamber type crystal oscillator (OCXO) and a temperaturecompensation type crystal oscillator (TCXO) can be exemplified. In theembodiment, the crystal oscillator 30 is used as an oscillator, but theinvention is not limited thereto. For example, an atomic oscillator maybe used as the oscillator.

The crystal oscillator 30 is configured to be able to minutely adjustthe frequency according to an output voltage (control voltage) of theloop filter 22. As described above, the phase comparator 21, the loopfilter 22, the DSP 23, and the frequency divider 24 completelysynchronize the clock signal output by the crystal oscillator 30 withthe 1 PPS output by the GPS receiver 10. That is, a configuration formedby the phase comparator 21, the loop filter 22, the DSP 23, and thefrequency divider 24 functions as a “synchronization control unit” thatsynchronizes the clock signal output by the crystal oscillator 30 withthe 1 PPS. The temperature sensor 40 is disposed near the crystaloscillator 30. The DSP 23 also performs a process of performingtemperature compensation of frequency temperature characteristics of thecrystal oscillator 30 by adjusting the output voltage of the phasecomparator 21 according to a detected value (detected temperature) ofthe temperature sensor 40.

As illustrated in FIG. 1, the control unit 31 includes a switch timingdecision unit 311. The switch timing decision unit 311 includes athreshold value storage unit 312. The control unit 31 is configured toinclude, for example, a CPU and a memory and controls, for example, anoperation of switching between the first and second standard signals inthe processing unit 20.

The prior information output unit 33 includes a prior informationgeneration unit 331, a prior information storage unit 332, and a timeinformation storage unit 333. The prior information generation unit 331includes the above-described GPS receiver 10.

In the timing signal generation device 1, the prior information isstored in the prior information storage unit 332 in advance and the 1PPS (standard signal) output from an output terminal electricallyconnected to the processing unit 20 to the outside is switched from oneof the first and second standard signals to the other based on the priorinformation. Hereinafter, “outputting the standard signal from theoutput terminal electrically connected to the processing unit 20 to theoutside” is simply referred to as “outputting the standard signal”.Further, “switching the standard signal from one of the first and secondstandard signals to the other” is simply referred to as “switching thestandard signal”.

The reason for switching the standard signal is, for example, that theposition of the GPS satellite 2 is bad, the accuracy of the 1 PPS outputby the GPS receiver 10 deteriorates, and thus the accuracy of the firststandard signal deteriorates. Accordingly, when the position of the GPSsatellite 2 is good, the first reference signal is output as thestandard signal. When the position of the GPS satellite 2 is bad, thesecond standard signal is output as the standard signal.

Information based on the position of the GPS satellite 2 can beexemplified as the prior information. The prior information isinformation which can be obtained in advance.

Specifically, examples of the prior information include positionalinformation indicating a relation between a time and the position of theGPS satellite 2 with respect to the reception point (the installationplace of the GPS antenna 50), DOP information indicating a relationbetween a time and dilution of precision (DOP) such as position dilutionof precision (PDOP), and reception sensitivity information indicating arelation between a time and reception sensitivity of the satellitesignal by the GPS receiver 10. Such information includes informationindicating deterioration or improvement in the accuracy of the satellitesignal such as the 1 PPS.

The “DOP” is a numerical value (index) indicating the degree ofdeterioration in the accuracy of the positioning based on the satellitesignals received by the GPS receiver 10, that is, an accuracydeterioration rate. The lower the DOP is, the better the accuracy is.Further, the “PDOP” is a subordinate concept of the DOP and is anumerical value (index) indicating the degree of deterioration in theaccuracy of the positioning based on the satellite signals received bythe GPS receiver 10, that is, a position accuracy deterioration rate.The lower the PDOP is, the better the accuracy is. In the embodiment, acase in which the DOP information is used as the prior information willbe described as a representative example. A relation between a time andthe DOP is not uniform every day and is shifted every day. Therefore,the prior information such as the DOP information is generated inaddition to the shift.

Next, a conversion timing of the standard signal will be described.

First, a threshold value indicating the lower limit of an allowablerange of the DOP is set. This threshold value is stored in advance inthe threshold value storage unit 312.

The threshold value is not particularly limited and is appropriately setaccording to all the conditions. The threshold value is preferably equalto or less than 3, is more preferably equal to or less than 2, and isstill more preferably equal to or greater than 1.05 and equal to or lessthan 1.5.

When the threshold value is greater than the upper limit of theallowable range, the accuracy of the first standard signal isinsufficient in some cases depending on other conditions.

The prior information output unit 33 outputs the DOP information to theswitch timing decision unit 311 of the control unit 31. Then, the switchtiming decision unit 311 decides the switch timing of the standardsignal in the following way based on the DOP information and thethreshold value, and the control unit 31 controls the operation of theprocessing unit 20 to switch the standard signal.

As illustrated in FIG. 4, times at which the DOP is the threshold valueare t2 and t3. In this case, the first standard signal is output untiltime t2 and is switched to the second standard signal at time t2. Thesecond standard signal is output from time t2 to time t3 and is switchedto the first standard signal at time t3. Then, the first standard signalis output from time t3.

By switching the standard signal based on the prior information in thisway, it is possible to typically output the reference signal with goodaccuracy and thus ensure the accuracy of the standard signal.

In the control of the switch of the standard signal, time t2 and time t3may be stored and the standard signal may be configured to be switchedat time t2 and time t3.

As described above, time t2 and time t3 may be switching times. However,in consideration of an error or the like, the standard signal ispreferably switched at a time earlier by predetermined time T1 than t2and at a time later by predetermined time T2 than t3. The times T1 andT2 are time information and are stored in advance in the timeinformation storage unit 333.

The prior information output unit 33 outputs the DOP information and thetime information to the switch timing decision unit 311 of the controlunit 31. Then, the switch timing decision unit 311 decides the switchtiming of the standard signal based on the DOP information, thethreshold value, and the time information, as will be described below,and the control unit 31 controls the operation of the processing unit 20to switch the standard signal.

That is, the first standard signal is output until time t1 and isswitched to the second standard signal at time t1. The second standardsignal is output from time t1 to time t4 and is switched to the firststandard signal at time t4. Then, the first standard signal is outputfrom time t4.

Accordingly, it is possible to output the standard signal with goodaccuracy more reliably, and thus it is possible to ensure the accuracyof the standard signal.

T1 and T2 are not particularly limited and are appropriately setaccording to all the conditions. T1 and T2 are preferably equal to orless than 30 minutes, are more preferably equal to or less than 15minutes, and are further more preferably equal to or greater than 1second and equal to or less than 5 minutes. T1 and T2 may be the same ormay be different.

When T1 and T2 are longer than the upper limit, the accuracy of thefirst reference signal is insufficient in some cases depending on otherconditions.

In the control of the switching of the standard signal, time t1 and timet4 may be stored. At time t1 and time t4, the standard signal may beconfigured to be switched.

In the timing signal generation device 1, the user obtains the DOPinformation before use of the DOP information, stores the DOPinformation in the prior information storage unit 332, stores thethreshold value in the threshold value storage unit 312, and stores thetime information in the time information storage unit 333. Needless tosay, any one, two, or all of the pieces of information may be stored inadvance.

In the timing signal generation device 1, the timing signal generationdevice 1 may be operated in advance, the prior information generationunit 331 may generate (create) the DOP information, and the DOPinformation may be stored in the prior information storage unit 332. Inthis case, the GPS receiver generates the DOP information based on thereceived satellite signals. As described above, the relation between atime and the DOP is not uniform every day and is shifted every day.Therefore, the prior information generation unit 331 generates the DOPinformation in addition to the shift. Accordingly, more accurate DOPinformation can be obtained.

In the timing signal generation device 1, when the DOP is equal to orless than the threshold value, information for obtaining a correctionvalue of aging correction of the crystal oscillator 30, that is,information regarding the control voltage of the crystal oscillator 30input from the loop filter 22 to the crystal oscillator 30, is acquired.The information regarding the control voltage is stored in a storageunit (not illustrated). When the DOP exceeds the threshold value, thecontrol voltage of the crystal oscillator 30 including the correctionvalue of the aging correction of the crystal oscillator 30 is obtainedbased on the information regarding the control voltage, the controlvoltage is input to the crystal oscillator 30, the crystal oscillator 30is caused to perform free-running, and the second standard signal isoutput to the outside. Accordingly, when the second standard signal isoutput, the aging correction of the crystal oscillator 30 can beperformed, and thus the temporal accuracy of the second standard signalcan be improved.

Specifically, as illustrated in FIG. 5, the information regarding thecontrol voltage of the crystal oscillator 30 output from the loop filter22 is acquired until time t2 at which the DOP is the threshold value.

When the DOP exceeds the threshold value, that is, from time t2 to timet3, the control voltage of the crystal oscillator 30 including thecorrection value of the aging correction of the crystal oscillator 30 isobtained based on the information regarding the control voltage untiltime t2. That is, the control voltage of the crystal oscillator 30 at acorresponding time is obtained based on a function (calculation formula)of a curve indicating a relation between a time and the control voltageof the crystal oscillator 30 until time t2 illustrated in FIG. 5. Then,the obtained control voltage is input to the crystal oscillator 30 fromtime t2 to time t3, the crystal oscillator 30 is caused to performfree-running, and the second standard signal is output to the outside.

The information regarding the control voltage of the crystal oscillator30 output from the loop filter 22 is acquired from time t3, as describedabove. When the DOP exceeds the threshold value, as described above, thecontrol voltage of the crystal oscillator 30 including the correctionvalue of the aging correction of the crystal oscillator 30 is obtainedbased on the information regarding the control voltage.

As described above, the DOP information is used in the timing signalgeneration device 1. Then, when the accuracy of the 1 PPS output by theGPS receiver 10 is high, the first standard signal with higher accuracythan the accuracy of the crystal oscillator 30 can be generated andoutput by synchronizing the clock signal output by the crystaloscillator 30 with the accurate 1 PPS output by the GPS receiver 10.

When the accuracy of the 1 PPS output by the GPS receiver 10 is low, thesecond standard signal with at least the frequency accuracy of thecrystal oscillator 30 can be output by stopping the process ofsynchronizing the clock signal output by the crystal oscillator 30 withthe 1 PPS output by the GPS receiver 10 and causing the crystaloscillator 30 to perform free-running.

Since the DOP information is stored in advance in the prior informationstorage unit 332 and the standard signal is switched based on the DOPinformation, the standard signal can be switched from the first standardsignal to the second standard signal before deterioration in theaccuracy of the 1 PPS output by the GPS receiver 10. Accordingly, it ispossible to typically output the reference signal with good accuracy andthus ensure the accuracy of the standard signal.

Since the accuracy of the standard signal can be ensured withoutdisposing the antenna 50 at a high position, it is possible to reducecost to that extent.

Second Embodiment

FIG. 6 is a diagram illustrating a schematic configuration of main unitsof a second embodiment of the timing signal generation device accordingto the invention. FIG. 7 is a graph illustrating a relation between atime and an accuracy deterioration rate of a satellite signal in thetiming signal generation device illustrated in FIG. 6.

In the second embodiment, differences from the above-described firstembodiment will be mainly described below and the description of thesame matters will be omitted.

As illustrated in FIG. 6, in the timing signal generation device 1according to the second embodiment, the GPS antenna 50 is installed inan outside surface 43 of a wall 42 of a building 41. The GPS antenna 50is disposed at a position lower than the height of the building 41.

In this case, depending on a period of time (time), some of the radiowaves sent from four GPS satellites 2 may be blocked by the building 41in some cases. In the example illustrated in FIG. 6, one of the radiowaves sent from the four GPS satellites 2 is blocked by the building 41during a predetermined period of time. Accordingly, one of the foursatellite signals is not received by the GPS receiver 10 via the antenna50, and the DOP becomes high.

In the timing signal generation device 1, the DOP information is storedas the prior information in advance in addition to the foregoingsituation in the prior information storage unit 332. As described in thefirst embodiment, the standard signal is switched. As illustrated inFIG. 7, in the embodiment, when the DOP is high, the standard signal isswitched accordingly four times in a day in the timing signal generationdevice 1.

In the embodiment, instead of the DOP information, for example,information indicating the period of time in which at least one of thesatellite signals sent from the four GPS satellites 2 may not bereceived by the GPS receiver 10 via the antenna 50 due to the fact thatat least one of the four GPS satellites 2 is at a dead angle for theantenna 50 may be stored as the prior information in advance in theprior information storage unit 332.

In this case, before a predetermined time of a time (timing) at whichthe dispositions of the GPS satellites 2 in which the four satellitesignals can be received are changed to the positions of the GPSsatellites 2 in which one satellite signal may not be received, thestandard signal is switched from the first standard signal to the secondstandard signal. In contrast to the foregoing, after a predeterminedtime of a time (timing) at which the dispositions of the GPS satellites2 in which one satellite signal may not be received are changed to thepositions of the GPS satellites 2 in which the four satellite signalscan be received, the standard signal is switched from the secondstandard signal to the first standard signal. As described in the firstembodiment, the predetermined time may be 0, that is, the predeterminedtime may not be provided. The predetermined time in the case of theswitching of the standard signal from the first standard signal to thesecond standard signal and the predetermined time in the case of theswitching of the standard signal from the second standard signal to thefirst standard signal may be the same or may be different.

In the timing signal generation device 1, it is possible to obtain thesame advantages as the above-described first embodiment.

2. Electronic Apparatuses

Next, an embodiment of an electronic apparatus according to theinvention will be described.

FIG. 8 is a block diagram illustrating an embodiment of an electronicapparatus according to the invention.

An electronic apparatus 300 illustrated in FIG. 8 includes a timingsignal generation device 310, a central processing unit (CPU) 320, anoperation unit 330, a read-only memory (ROM) 340, a random access memory(RAM) 350, a communication unit 360, and a display unit 370.

The timing signal generation device 310 is, for example, the timingsignal generation device 1 according to any one of the first and secondembodiments described above. As described above, the timing signalgeneration device 310 receives the satellite signals, generates thehighly accurate timing signal (1 PPS), and outputs the timing signal tothe outside. Accordingly, the electronic apparatus 300 with highreliability can be realized at low cost.

The CPU 320 performs various calculation processes and control processesaccording to programs stored in the ROM 340 or the like. Specifically,to perform a clocking process in synchronization with a timing signal (1PPS) or a clock signal output by the timing signal generation device310, various processes according to operation signals from the operationunit 330, and data communication with the outside, the CPU 320 performs,for example, a process of controlling the communication unit 360 and aprocess of transmitting a display signal for displaying various kinds ofinformation to the display unit 370.

The operation unit 330 is an input device configured to include anoperation key or a button switch and outputs an operation signalaccording to an operation by a user to the CPU 320.

The ROM 340 stores data or programs used for the CPU 320 to performvarious calculation processes or control processes.

The RAM 350 is used as a work area of the CPU 320 and temporarilystores, for example, data or a program read from the ROM 340, data inputfrom the operation unit 330, and calculation results obtained when theCPU 320 executes various programs.

The communication unit 360 performs various kinds of control toestablish data communication between the CPU 320 and an external device.

The display unit 370 is a display device configured to include a liquidcrystal display (LCD) and displays various kinds of information based ondisplay signals input from the CPU 320. A touch panel functioning as theoperation unit 330 may be installed in the display unit 370.

Any of various electronic apparatuses is considered as the electronicapparatus 300 and the invention is not particularly limited thereto.Examples of the electronic apparatus include a server (time server) fortime management realizing synchronization with a standard time, a timemanagement apparatus (timestamp server) performing issuing of atimestamp or the like, and a frequency standard apparatus such as a basestation.

The timing signal generation device and the electronic apparatusaccording to the invention have been described according to theillustrated embodiments, but the invention is not limited thereto. Theconfiguration of each unit can be substituted with any configurationhaving the same function. Any other constituent element may be added.

The invention may be a combination of the configurations(characteristics) of any two or more of the above-described embodiments.

In the foregoing embodiments, the timing signal generation device usingthe GPS has been exemplified. However, the invention is not limited tothe GPS, but a Global Navigation Satellite System (GNSS) other than theGPS, for example, Galileo or GLONASS, may be used.

What is claimed is:
 1. A timing signal generation device comprising: anoutput terminal that outputs a standard signal; a first standard signalgeneration unit that generates a first standard signal based on areference signal input from outside; a second standard signal generationunit that generates a second standard signal based on a signal outputfrom an oscillator; and a control unit that switches the standard signaloutput from the output terminal from the first standard signal to thesecond standard signal based on prior information indicating thataccuracy of the reference signal deteriorates.
 2. The timing signalgeneration device according to claim 1, further comprising: a priorinformation output unit that outputs the prior information to thecontrol unit.
 3. The timing signal generation device according to claim2, wherein the prior information output unit includes a priorinformation storage unit that stores the prior information.
 4. Anelectronic apparatus comprising: the timing signal generation deviceaccording to claim
 3. 5. The timing signal generation device accordingto claim 2, wherein the prior information output unit includes a priorinformation generation unit that generates the prior information basedon the reference signal.
 6. An electronic apparatus comprising: thetiming signal generation device according to claim
 5. 7. The timingsignal generation device according to claim 2, further comprising: atime information storage unit that stores time information, wherein thecontrol unit includes a switch timing decision unit that decides aswitch timing of the standard signal based on the prior information andthe time information.
 8. The timing signal generation device accordingto claim 7, wherein the reference signal is a satellite signaltransmitted from a position information satellite, wherein the priorinformation output unit outputs dilution of precision informationindicating a relation between a time and an accuracy deterioration rateof positioning based on the reference signal as information indicatingthat the accuracy of the reference signal deteriorates to the switchtiming decision unit, and wherein the switch timing decision unitincludes a threshold value storage unit that stores a threshold valueand decides the switch timing of the standard signal based on thethreshold value and the dilution of precision information.
 9. The timingsignal generation device according to claim 8, wherein the oscillator isa voltage control oscillator, wherein the first standard signalgeneration unit inputs a control voltage of the oscillator to theoscillator and generates the first standard signal based on thereference signal when the accuracy deterioration rate is equal to orless than the threshold value, and wherein the control unit acquiresinformation regarding a control voltage of the oscillator input to theoscillator when the accuracy deterioration rate is equal to or less thanthe threshold value, and the control unit obtains a control voltageinput to the oscillator based on the acquired information regarding thecontrol voltage and inputs the obtained control voltage to theoscillator to switch the reference signal output from the outputterminal from the first standard signal to the second standard signalwhen the accuracy deterioration rate exceeds the threshold value.
 10. Anelectronic apparatus comprising: the timing signal generation deviceaccording to claim
 9. 11. An electronic apparatus comprising: the timingsignal generation device according to claim
 8. 12. An electronicapparatus comprising: the timing signal generation device according toclaim
 7. 13. An electronic apparatus comprising: the timing signalgeneration device according to claim
 2. 14. The timing signal generationdevice according to claim 1, wherein the reference signal is a satellitesignal transmitted from a position information satellite, and whereinthe first standard signal generation unit includes a receiver thatreceives the satellite signal.
 15. An electronic apparatus comprising:the timing signal generation device according to claim
 14. 16. Thetiming signal generation device according to claim 1, wherein the priorinformation includes information indicating that the accuracy of thereference signal improves, and wherein the control unit switches thestandard signal output from the output terminal from the second standardsignal to the first standard signal based on the prior information. 17.An electronic apparatus comprising: the timing signal generation deviceaccording to claim
 16. 18. An electronic apparatus comprising: thetiming signal generation device according to claim
 1. 19. A timingsignal generation device that switches, based on prior informationindicating that accuracy of a reference signal input from outsidedeteriorates, a signal used to generate a standard signal from thereference signal to a signal output from an internal oscillator.
 20. Anelectronic apparatus comprising: the timing signal generation deviceaccording to claim 19.